INTERACTIONS OF WIDE-BAND GAP SINGLE-CRYSTALS WITH 248 NM EXCIMER-LASER RADIATION .3. THE ROLE OF CLEAVAGE-INDUCED DEFECTS IN MGO

When single-crystal, arc-fused MgO is cleaved and exposed to single pulses of 248 nm, 3-10 J/cm2 excimer laser light (in vacuum), micron-sized holes are produced in the irradiated area. Cleavage produces micron-sized sites which exhibit highly localized absorption, resulting in decomposition, melting, and vaporization of the crystal at these sites. At fluences between 1 and 2 J/cm2, single laser pulses can produce localized, superficial melting and decomposition, leaving clusters of Mg-rich droplets on the surface. The mass-resolved charged and neutral particle emission produced by irradiation of the cleaved MgO surface with single laser pulses are examined. There are considerable variations in these emissions when single laser pulses strike different regions of the cleavage surface; these variations are strongly correlated with the production of conical holes in the irradiated region. A phenomenological model for the creation of these sites involving dislocation driven processes during cleavage and the resulting interactions of these sites with the laser beam are presented.